It appears that changing a model to a co-creator changes the price of some of the materials. I have confirmed this by changing another model of mine from normal to co-creator and back. The prices were as expected when the model was normal and were inflated when co-creator. I have not been able to derive a relationship which would indicate how the prices are being modified. The increase does not appear to be a percentage or static value. The main oddity I see is that the co-creator prices are generally rounded to the a 5-cent boundary.

As an additional example (beyond what is posted in that other thread), the model I switched tonight went from ~$303 for stainless steel to $350. The heart ornament (my previous discovery) went from $40 to $50.

1. Is this behavior intentional?
1.a. If the behavior is intentional, is it documented anywhere?
1.a.1. If the behavior is not documented anywhere, why not? I have been generally pleased with Shapeways' communications - let's keep things like this in the open.
1.a.2 If the behavior is documented somewhere, where is it?
1.b. If the behavior is not intentional, when will it be corrected?

Ah - that checks out. May I suggest adding that comment somewhere in the Co-Creator Support page? Now that you've said it, it makes sense (since the charging is done before the final object is created), but I'd love to see that documented with other Co-Creator information.

And it looks like I need to put the Co-Creator max volume closer to the size of the actual model. I allowed some buffer, but it is unnecessary buffer.

I am having the same exact issue. I purchased 10 copies of a charm in stainless steel for $2.80 each. Now they are $8.24 each. That's a HUGE difference. I purchased the same item in gold plate for $20 and now it comes up at $11.24. I don't get it and I really would like to know what the explanation is as it's holding me up from placing an order for stainless steel.

That is a big difference, but consider that someone has to physically handle these objects midway through the process for stainless steel. With something that size, I imagine it's pretty tricky. From the discussion on the (overly long) price thread, I gather that adding sprues for metal pieces probably will not make life easier, since the sprue is likely to break during cooling.

I'm sorry that your item went up by so much, but consider the unique nature of what's being done here.